Method and apparatus for assembling photo tubes



C. L. DAY

March 20, 1962 Filed June 25, 1959 w .4 a n a MNA/ a u 4 n n M /lblIY if ...Wl uw n e a w a W 6 United States Patent Oiiice 3,026,163 Patented Mar. 20, 1952 3,026,163 NEYI'HOD AND APPARATUS FOR ASSEMBLING PHOTO TUBES Cyril L. Day, Huntington, Ind., assignor to International Telephone and Telegraph Corporation Filed .lune 25, 1959, Ser. No. 822,833 7 Claims. (Cl. 316--21) This invention relates generally to photo tubes and more particularly to a method and apparatus for forming and sensitizing a photocathode on the face plate portion of the tube prior to its assembly on the body portion and for thereafter joining the two portions.

An image tube is a common form of photo tube, conventionally comprising an evacuated envelope or body having a photocathode formed at one end and a phosphor viewing screen formed at the other end. In the past, the photocathode of such tubes has conventionally been formed and sensitized or activated after assembly and evacuation of the tube; this has required that the evaporator which deposits metal, typically silver, on the faceplate together with the source of activating vapor, typically cesium, be located in the tube itself. Since the cesium vapor conventionally employed for activating the photocathode will contaminate the phosphor screen and other tube elements which may be provided between the phosphor screen and the photocathode, it has, in the past, been necessary to isolate the source of cesium vapor from the phosphor screen and other tube elements, and numerous mechanically complex shutter arrangements have been provided for this purpose. ln addition, in such prior photo tube constructions, it is obvious that the photocathode forming and activating source remains in the finished tube, that external terminals are required on the tube body for making the necessary electrical connections to the photocathode forming and activating sources, and finally that the conventional exhaust tubulation must be provided on the tube body.

It has in the past been proposed to provide a photo tube construction in which the photocathode is formed on the faceplate and activated prior to assembly of the faceplate portion on the body portion of the tube, thus permitting elimination of shutter arrangements for isolating the source of cesium vapor from the phosphor screen and other elements of the tube and also permitting elimination of the external terminals previously required for making connections to the photocathode forming and activating sources. However, to the best of the present applicants knowledge, no satisfactory apparatus or method for thus assembling a photo tube has been proposed.

lt is accordingly an object of my invention to provide an improved apparatus for assembling a photo tube.

Another object of my linvention is to provide an improved method for assembling a photo tube.

A further object of my invention is to provide an improved apparatus for assembling a photo tube in which the photocathode is formed on the faceplate portion of the tube and activated prior to assembly of the faceplate portion on the body portion of the tube.

A still further object of my invention is to provide an improved method for assembling a photo tube in which the photocathode is formed on the faceplate portion of the tube and activated prior to assembly of the faceplate portion on the body portion of the tube.

In accordance with the broader aspects of my invention, a photo tube is constructed with separate faceplate and body portions joined by mating metal flanges. In accordance with the improved method of my invention, the faceplate portion and body portion of the tube are initially positioned in separate but communicating containers or compartments which are then evacuated. The

photocathode is then deposited on the inner surface of the faceplate and activated in its compartment and is then transferred to the other compartment where it is positioned so as to close the body portion and with its flange engaging the ange ofthe body portion. The two flanges are then joined, preferably by a cold pressure weld, after which the vacuum is released and the completed tube removed. The improved apparatus of my invention comprises a bell jar having two compartments joined by a passage for supporting the faceplate portion for movement between a first position closing one compartment with the inner surface thereof exposed thereto and a second position in the opening of the other compartment. Means are provided for evacuating both compartments and the passage of the bell jar, and means are positioned in the one compartment for forming and activating the photocathode on the inner surface of the faceplate portion when it is in its first position. A rst annular die member is provided positioned in the other compartment and proportioned to support the llange of the body portion and having a cavity formed therein for accommodating the `body portion so that the faceplate portion in its second position closes the body portion with the flanges being respectively in engagement. A second annular die member is provided positioned in the other compartment and proportioned to engage the llange of the faceplate portion in its second position, the die members being relatively movable and respectively cooperating to join the flanges of the faceplate and body portions.

The above mentioned and other features and objects of this invention and the manner of attaining them will become more apparent and the invention itself will be best understood by reference to the following description of an embodiment of the invention taken in conjunction with the accompanying drawings, wherein:

FIG. l is a cross-sectional view illustrating the improved apparatus and method of my invention;

FIG. 2 is a top view of a bottom section of the bell jar assembly of the apparatus of FIG. l; and

FiG. 3 is a cross-sectional View of a completed photo tube assembled in the apparatus of and in accordance with the method of my invention.

Referring now to the figures of the drawing, the apparatus of my invention, generally identified at 10 comprises a bell jar assembly 11 having a body portion formed of mating top and bottom sections 12 and 13. Top and bottom sections 12 and 13, which are preferably formed of steel, have mating elongated channels 14 and 15 formed therein which define an elongated passage 16 having a generally flat bottom surface when top and bottom sections l2 and 13 are assembled as shown in FIG. l. Bell jar 11 is provided with two containers or compartments 17 and 18 respectively communicating with passage 16 adjacent its ends 19 and 21, as shown. It will be seen that the opening 22 communicating between end 19 of passage 16 and the compartment 17 is smaller than the inside diameter of compartment 17. Top and bottom sections 12 and 13 of bell jar 11 are secured together by means of suitable threaded fasteners 23, with a vacuum-tight seal being provided in any suitable manner, such as by an annular copper ring 24, as shown.

Compartment 17 is the photocathode forming compartment, and has a suitable window 25 formed in its bottom facing opening 22 to assist in the photocathode formation. An evaporator cup 26 is positioned in compartment 17, being suspended from and removably secured to opening 22 in the bottom surface of channel 1S, as shown. Evaporator cup 26 has an opening 27 in its bottom end defined by an annular ange 28, opening 27 being in alignment with the window 25 and the opening 22. A pair of spaced apart metal rings 29 and 31 are provided in the evaporator cup 26, the bottom ring 29 being supported on the annular flange 2S and the upper ring 31 being secured to the bottom ring 29 by means of a plurality of stand-off insulators 32. An annular evaporator 33 is supported on the uppei` surface of the ring 31 facing the opening 22, as shown. One or more vapor producing channels 34 is provided having its bottom end connected to the bottom ring 29 and its top end connected to a ribbon electrical lead 35 extendin through the top ring 31 and insulated therefrom by a suitable insulator 36. The ribbon electrical lead 35 from Vthe vapor producing channel 34 and ribbon electrical lead 37 from evaporator 33 are carried out of evaporator cup 26 by means of suitable insulators 38 and through insulators 39, attached to the inner wall of compartment 17, and in turn through the wall of compartment 17 by means of insulators 41. lt will be Yreadily seen that when the top section 12 of bell jar 11 is removed from the bottom section 13, the evaporator assembly may be removed for cleaning and replacement of the photocathode formation materials by clipping the ribbon leads 35 and 37 which permits the leads to be pushed through insulators 3S thus permitting removal of evaporator cup through opening 22. ln order to replace the evaporator cup 25 in compartment 17, new ribbon leads can be welded to the portions extending out of insulators 39 and fed through the insulators 38.

The particular photo tube adapted to be assembled in the apparatus of FIG. 1 is shown in FlG. 3, and comprises a faceplate portion 42 and an envelope or body portion 43. Faceplate portion 42 includes a transparent faceplate 44 having a photocathode formed on its inner surface 45, while body portion 43 has a phosphor screen 46 formed in the inner surface of its end wall 47; conventional focusing electrodes (not shown) are also provided. Faceplate portion 42 and body portion 43 are joined together by mating annular metal flanges 48 and 49 respectively secured to faceplate 44 and body portion 43, as shown. Annular metal flanges 48 and 49, which preferably are formed of copper, are preferably generally cup-shaped with flange 4S facing away from the inner surface 45 of faceplate 44 and flange 49 facing away from the open end of the body portion 43, as shown.

Referring back to FIG. l, it will be observed that the faceplate portion 42 of photo tube 40 is initially positioned in passage 16 at end 19 with flange 48 resting on the bottom surface `'of channel 15 so-that faceplate 44 closes opening 22 communicating with compartment 17 and with inner surface 45 of faceplate 44 being in alignment with window 25 of compartment 17 and the evaporator cup 26 and window 56.

ln order to clamp faceplate portion 42 in the position shown in FIG. l in order to segregate the photocathode activating vapor, such as cesium, from the rest of the bell jar, an opening 51 is provided in the top section 12 of bell vjar 11 in alignment with opening 22 in bottom section 13. A tubular member 52 is positioned in opening 51 extending upwardly therefrom, tubular member 52 having a diameter proportioned so that tubular member 52 can be seated -on the radially inner portion 53 of annular flange 48, thus clamping the same tightly against the bottom suiface of channel 15. The upper end 54 of tubular member 52 is attached to a top plate 55 which has another window 56 formed therein in alignment with and facing the faceplate 44, window 56 also assisting in the photocathode formation. Top plate 55 is sealed to top section 12 of bell jar 11 in vacuum-tight relationship by a suitable collapsible bellows 57 which thus accommodates the movement of the tubular member 52.

Compartments 17 and 18 are respectively provided with exhaust tubulations 58 and 59 as shown, and it will thus be readily comprehended that when the two compartments and the connecting passage 16 are evacuated, tubular member 52 will be moved downwardly in the direction shown by the arrow 61 so that its lower end 62 engages inner section 53 of annular ange 4S, thereby tightly clamping the faceplate portion 42 in its photocathode-forming position, as shown in FIG. l. 1n order to release the clamping action of tubular member 52 so as to transfer the faceplate portion 42 to the other compartment 18, as will be hereinafter described, studs 63 are provided extending upwardly from the top section 12 of bell jar 11 and threadingly engaging openings 64 in the top plate 55. Thus, studs 63 can be utilized to lift top plate and thus in turn tubular member 52 away from annular ange 48 of faceplate portion 42 against the vacuum in compartments 17 and 18 and in passage 16.

Compartment 18 has an annular pinch-off die 65 positioned therein and removably secured thereto, as by threaded connection 66. The working surface 67 of stationary die part is arranged to support the outer periphery 68 of annular ilange 49 of body portion 43, with body portion 43 being accommodated in cavity 69 formed in the fixed annular die part 65. It will be observed that the working surface 67 of annular die 65 is disposed slightly below the bottom surface of channel 15 of bottom section 13 of bell jar assembly l1 so that the outer surface 68 of annular ange 49 is generally Hush with the bottom surface of channel 15.

Movable annular pinch-off die part 71 is positioned in opening 72 in top section 12 of bell jar assembly 11, opening 72 being in alignment with compartment 18. Movable die part 71 is secured to an upper part 73 by a suitable threaded fastening 74, upper part 73 being sealed to the top section 12 of bell jar assembly 11 in vacuumtight relationship by another suitable collapsible bellows 75 which thus accommodates movement of the movable die member 71. In order to retain the movable die member 71 out of cooperative engagement with the fixed die member 65, a suitable bracket 76 may be provided SGCHrd t0 the upper die part '73 by a suitable threaded fastener 77, as shown.

In accordance with the method of my invention, the top section 12 of bell jar 11 and the elements connected thereto is removed from bottom section 13 with faceplate portion 42 initially being positioned in passage 15 closing opening 22, as shown, and with body portion 43 being positioned in compartment 1S with flange 49 supported on working surface 67 of die 65, as shown. Top section 12 of bell jar assembly 11 is then assembled on bottom section 13 and sealed thereto. Exhaust tubulations 58 and 59 of compartments 17 and 18 are then connected to a suitable vacuum pumping system which evacuates both compartments and passage 16; it will be observed Y that since each compartment of the compartments 17 and 13 has its own exhaust tubulation 58 and 59 respectively, the two compartments 17 and 18 can be isolated by placing a cold trap between them during pumping as is well known to those skilled in the art. Studs 63 may then be manipulated permitting tubular member 52 to move downwardly in the direction shown by the arrow 61 under the influence of the vacuum in passage 16 so that its lower end 62 rmly engages inner portion 53 of annular ange 4S of faceplate portion 42. After the desired vacuum has been obtained, the assembly, which may have been located in an oven, may be run through an appropriate baking cycle as required for the particular tube. The assembly is then cooled and the photocathc-de formation carried on in the usual way. Evaporator 33 is connected to a suitable source of power, thereby to evaporate the desired metal, such as silver, on the inner surface 45 of faceplate 44 following which the Vapor producing channel 44 is connected to a suitable source 0f potential thereby to produce the desired vapor, typically cesium, which is deposited on the silver coating formed on the inner surface 45 of faceplate 44 thereby activating the same. lt will thereby be readily understood that the particular photocathode and its method of activation does not form a part of my .present invention, and therefore that other or additional vapor producing channels may be provided.

After formation and activation of the photocathode has been completed, the vacuum tubulations 58 and 59 of compartments 17 and 18 are sealed o and the bell jar 11 is removed from the pumping system, with the vacuum, however, being maintained in the compartments 17 and 18 and passage 16. Bellows 57 are then expanded by manipulating studs 63 to raise top plate 55 thereby freeing faceplate portion 42. Faceplate portion 42 is then transferred to compartment 18 by slightly tilting the bell jar assembly 11; it will be understood that the bottom surface of the channel 15 in bottom section 13 of bell jar assembly 11 is relatively at, thus in essence forming a track, permitting faceplate portion 42 to slide from a first position closing opening 22 to compartment 17 to a second position closing body portion 43 as will now be described. lt will now be observed that when faceplate portion 42 has been transferred to end 21 of passage 16, ange 48 will drop into and nest with ange 49 as shown in FIG. 3. Threaded fastener 77 is then removed permitting bellows 75 to collapse under the influence of the vacuum in compartment 18 and passage 16, thus firmly pressing working surface 78 of movable die 71 against outer portion 79 of flange 48 and in turn pressing flange 48 of the faceplate portion 42 firmly into engagement with flange 49 of body portion 43.

Bracket 76 is then removed and extensions 81 and 82 on pinch-off die members 65 and 71 are then placed in a suitable hydraulic press. Suitable pressure to join outer portions 68 and 79 of anges 48 and 49 by cold pressure welding, such as from ten to fifty tous of pressure, is then applied by the press. As will be seen in FIG. 3, outer portions 79(a) and 6801) of flanges 48 and 49 may respectively spread outwardly deining a V as the result of the cold pressure welding o eration or, alternatively, dies 65 and 71 may completely pinch-off the end portions 79 and 68 as indicated by the dashed lines 83 in FIG. 3. It will be seen that the provision of the -mating cup-shaped anges 48 and 49 not only permits accurate centering of faceplate portion 42 on body portion 43, but also tends to prevent outward buckling when the pressure is applied to the die parts, as is encountered with flat flanges. It will also be seen that the flanges serve as a radiator for the photocathode..

Exhaust tubulations 58 and 59 are then opened breaking the vacuum in the bell jar 11, threaded fasteners 23 are removed and the top section 12 is then removed from the bottom section 13 of bell jar assembly 11, with the resulting sealed tube 40 then being removed from the compartment 18. After cleaning the evaporating cup 26 and renewing the photocathode forming materials and tubulations, the bell jar assembly 11 is then again ready for use.

lt will now be readily observed that the tube 40 produced with my apparatus and in accordance with my method completely eliminates the gates and shutter devices previously required to isolate the photocathode forming sources from the phosphor display screen. Furthermore, it will be observed that since the photocathode was formed prior to assembly of the faceplate portion 42 and the body portion 43, the external electrical terminals in the body portion 43 formerly needed to make connection to the photocathode forming devices and for other tube processing are no longer necessary, and it will further be observed that since the faceplate portion 42 is assembled on the body portion 43 in a vacuum, the resulting tube is already evacuated, thereby eliminating the requirement for a conventional exhaust tubulation in the body portion 43. 1n addition, free cesium is completely eliminated in the finished tube and thus cold emission is reduced, the tube can be operated at higher voltages, and screen ediciency is increased.

While I have described above the principles of my invention in connection with specific apparatus, it is to be clearly understood that this description is made only by way of example and not as a limitation to the scope of my invention.

What is claimed is:

l. The method of assembling a photo tube of the type having separate faceplate and body portions respectively having mating annular metal flanges joining said portions and with the inner surface of the faceplate portion having a photocathode formed thereon comprising the steps of: initially positioning said faceplate portion in a iirst compartment; initially positioning said body portion in a second compartment which communicates with the first compartment; simultaneously evacuating both of said compartments; forming a photocathode on said inner surface 0f said face plate while the same is in said rst compartment; transferring said faceplate portion to said second compartment and positioning the same to close said body portion with said flanges respectively in engagement; joining said anges while said faceplate and body portions are in said second compartment in vacuum by cold pressure welding; and releasing the vacuum and removing the assembled tube from said second compartment.

2. The method of assembling a photo tube of the type having separate faceplate and body portions respectively having mating annular metal anges joining said portions and with the inner surface of the faceplate portion having a. photocathode formed thereon comprising the steps of: initially positioning said faceplate portion in a ii-rst compartment of a bell jar; initially positioning said body portion in a second compartment of said bell jar; evacuating said bell jar; forming a photocathode on said inner surface of said faceplate while the same is in said first compartment; transferring said faceplate portion to said second compartment and positioning said faceplate portion to close said body portion with their franges respectively engaging; joining said anges in said second compartment; and releasing the vacuum and opening said bell jar.

3. The method of assembling a photo tube of the type having separate faceplate and body portions respectively having mating annular metal flanges joining said portions and with the inner surface of the faceplate portion having a photocathode formed thereon comprising the steps of:` initially positioning said faceplate portion to close a first compartment of a bell jar with said inner surface exposed thereto; initially positioning said body portion in a second compartment of Said bell jar with the flange of said body portion being seated on a rst die member; evacuating said bell jar; forming a photocathode on the inner surface of said faceplate while the same closes said rst compartment; shifting said faceplate portion to said second compartment and positioning said faceplate portion to close said body portion with their anges respectively engaging; relatively moving said rst die member and a second die member so that said second die member is in engagement with the flange of said faceplate portion; applying pressure on said die members to join said flanges with a cold pressure weld; and releasing the vacuum and opening the bell jar.

4. The method of assembling a photo tube of the type having separate faceplate and body portions respectively having mating annular metal anges joining said portions and with the inner surface of the faceplate portion having a photocathode formed thereon comprising the steps of: positioning said faceplate portion in a passage in a bell jar with its ange supported by said passage and with said faceplate portion closing a first compartment which communicates with said passage and having said inner surface exposed to said first compartment; positioning said body portion in a second compartment of said bell jar which communicates with said passage with the flange of said body portion being seated on a irst die member; evacuating said bell jar and tightly clamping the ange of said faceplate portion against the wall of said passage with which said rst compartment communicates; evaporating a photocathode on the inner surface of said lfaceplate and sensitizing the same from a source in said first compartment; releasing said clamping; terminating said evacuating and maintaining -the vacuum; shifting said faceplate portion through said passage to said second compartment to close said body portion and with said flanges respectively engaging; relatively moving said first die member and a second die member so that said second die member is in engagement with the flange of said faceplate portion; applying pressure on said die members to join said anges With a cold pressure weld; and releasing the vacuum and Yopening the bell jar.

5. The method of assemblin" a photo tube comprising the steps of: providing a faceplate portion which is to have a photocathode formed on one surface thereof and which is secured to a `first generally cup-shaped annular metal ange which faces away from said one surface; providing a body portion to which said faceplate portion is to be joined and which has its open end secured to a second generally cup-shaped annular metal flange which faces away from said open end and which mates with said first flange; positioning said faceplate portion in a iirst container with said one surface facing the same and isolating said faceplate portion from a second container which communicates with said first container; positioning said body portion in said second container with said open end and second ange facing the opening thereof; evacuating both of said containers; depositing and activating a photocathode on said one surface of said faceplate portion from a source located in said lirst container; transferring said faceplate portion from said iirst container to said second container and positioning the same to close said body portions with said first ange nesting in said second ange; joining the outer peripheral extremities of said flanges with a cold pressure Weld; and releasing the vacuum and removing the assembled photo tube.

6. The method of assembling a photo tube of the type having separate faceplate and body portions with the inner surface of the faceplate portion having a photocathode formed thereon comprising the steps of: initially positioning said faceplate portion in a rst compartment; initially positioning said body portion in a second compartment which communicates with the first compartment; simultaneously evacuating both the said compartments; forming a photocathode on said inner surface of said faceplate while the same is in said rst compartment; transferring said faceplate portion to said second compartment and positioning the same to close said body portion; sealing said faceplate portion to said body portion; and releasing the vacuum and removing the assembled tube from said second compartment.

7. The method of assembling a photo tube of the type having separate faceplate and body portions respectively having mating annular metal flanges joining said portions and with the inner surface of the faceplate portion having a photocathode formed thereon comprising the steps of: positioning said faceplate portion in a passage in a bell jar with its ange supported by said passage and with said faceplate portion closing a first compartment which communicates with said passage and having said inner surface exposed to said first compartment; positioning said body portion in a second compartment of said bell jar which communicates with said passage with the ange of said body portion being seated on a first die member; evacuating said bell jar and tightly clamping the ange of said faceplate portion against the wall of said passage with which said first compartment communicates; evaporating a photocathode on the inner surface of said faceplate and sensitizing the same from a source in said rst compartment; releasing said clamping; shifting said faceplate portion through said passage to said second compartme-nt to close said body portion and with said anges respectively engaging; relatively moving said first die member and a second die member so that said second die member is in engagement with the flange of said faceplate portion; applying pressure on said die members to join said anges with a cold pressure weld; and releasing the vacuum and opening the bell jar` References Cited in the file of this patent UNITED STATES PATENTS 1,651,386 Gustin Dec. 6, 1927 2,162,209 Trutner June 13, 1939 2,561,404 Nordquist July 24, 1951 2,721,108 Lewin Oct. 18, 1955 2,807,517 Marschka et al. Sept. 24, 1957 2,837,396 Warren June 3, 1958 2,874,523 Ryan Feb. 24, 1959 

